On a work surface, using a chef’s knife or kitchen shears, cut out the backbone of each chicken and butterfly them.
Place the chickens in a large glass baking dish. Sprinkle with the dry rub, then rub with a lemon half. Cover with plastic wrap and let chill in the refrigerator for 12 hours.
Preheat half of the grill, setting the burners to high. Oil the side of the grill that is off.
Place the chickens on the side of the grill that is off, skin side down. Close the lid and cook for 45 minutes. Turn the chickens and cook for 35 minutes longer, or until a thermometer inserted into the thigh, without touching the bone, reads 180°F (82°C). During cooking maintain a grill temperature of 400°F (200°C). Transfer to a plate.
If desired, carefully remove the skin of one of the chickens. Dab the skin with a paper towel.
In a small pot over medium heat, heat 1 inch (2.5 cm) of oil. Fry one quarter of the skins at a time until crispy. Watch out for splattering. Drain on a paper towel. On a cutting board, chop the crispy skin.
Cut the chickens into 8 pieces each. Arrange the chicken pieces on a platter and sprinkle with the crispy skin. Serve with quick barbecue sauce (see recipe), if desired.